1. Field of the Invention
The invention relates to a mobile magnetometry processing system which improves the performance of mobile magnetometers through improved signal processing techniques which provide better separation of the spatial and temporal portions of ambient fields. A high degree of control over the spatial response function is provided. Responses corresponding to an aperture greater than that implied by the length of the sensor's string can be obtained. The magnetic field in the vicinity of the surface of the Earth is divided into two major components. These are:
(1) A time-varying component due to magnetic storms, lightning, circulating currents in the ionosphere, etc. This component will be referred to herein as the temporal component.
(2) A relatively steady component whose value depends on the location at which it is measured. This component is due to mineral deposits, large magnetic objects, etc. This component will be referred to herein as the spatial component.
2. Description of the Prior Art
Measurements of the spatial component of the magnetic field are of interest for applications including mineral prospecting and locating ferrous objects. Such measurements are made from a mobile platform such as an aircraft to permit the magnetic sensor to scan a significant geographic region. Since the output of a sensor moving through a spatially patterned field will be a time-varying signal, it is difficult to separate these spatially related components from the temporally induced components which would cause a time-varying signal even if the sensor were stationary. Separating these components is a major problem in mobile magnetometry. In addition, it is generally desired to examine the detailed local structures of the spatial component with minimal interference from its gross variation over large distances.
Prior art attempts to solve these problems have generally involved differencing the outputs of a pair of magnetometers to measure the gradient of the field. This provides good rejection of temporal components but greatly constrains the spatial response function of the instrument. It is also possible to compare the outputs of fixed and moving magnetometers. This, however, restricts the search area to the vicinity of the fixed magnetometer. A slow search with a single magnetometer will provide time averaging over the temporal component. It is also possible to average over successive passes, or scans, through the same search area. Both of these approaches result in greatly increased search time.